Preparation of nitroalkanes from alkyl nitrates and alkali metal nitrites



PREPARATION OF NITROALKANES FROM ALKYL NITRATES AND ALKALI METAL NITRITES Gustave Bryant Bachman, Lafayette, Ind., and Neil W.

Connon, Rochester, N.Y., assignors to Purdue Research Foundation, Lafayette, Ind., a corporation of Indiana No Drawing. Filed Dec. 18, 1967, Ser. No. 691,203

Int. Cl. C07c 79/04 U.S. Cl. 260-644 10 Claims ABSTRACT OF THE DISCLOSURE A process for preparing nitroalkanes by reacting a primary or secondary alkyl nitrate and an alkali metal nitrite in the presence of an inert solvent.

SUMMARY OF THE INVENTION This invention relates to a process for the preparation of nitroalkanes. In a particular aspect, this invention relates to a process for the preparation of nitroalkanes by reaction of a primary or secondary alkyl nitrate and an alkali metal nitrite in the presence of an inert solvent. In a further aspect, this invention relates to a process for the preparation of nitroalkanes by reaction of a primary or secondary alkyl nitrate and an alkali metal nitrite in the presence of an inert solvent and a nitrite ester scavenger.

Nitroalkanes are commonly prepared by the nitration of an aliphatic hydrocarbon with nitric acid in either the liquid or the vapor phase. The nitric acid nitration procedure results in the production of a mixture of nitro alkanes. Also, this procedure is generally not suitable for the production of the higher nitroalkanes; that is to say, nitroalkanes having more than about 4 carbon atoms.

Nitroalkanes have also been prepared by the reaction of an alkyl halide and sodium nitrite. This procedure is based on studies conducted by Kornblum et al. and is discussed in detail in Journal of the American Chemical Society, 78, 1497-1501 (1956) and in Journal of Organic Chemistry, 22, 455 (1957). The reported procedure results in the preparation of a single nitroalkane and may be used to obtain higher nitroalkanes. Despite these significant advantages, it has not proven generally suitable, principally because of the difiiculty in obtaining the alkyl halide starting material, especially the secondary alkyl halide, in relatively pure form.

It is an object of the present invention to provide a process for the preparation of nitroalkanes.

It is a further object of the present invention to provide a process for the preparation of nitroalkanes by which a single nitroalkane is obtained.

It is a still further object of the present invention to provide a process for the preparation of higher nitroalkanes.

It is an additional object of the present invention to provide a process for the preparation of nitroalkanes from alkyl nitrates.

Other objects and advantages of the present invention will be apparent from the specification and appended claims.

It has been discovered in accordance with the present invention that nitroalkanes are obtained by reacting an alkyl nitrate with an alkali metal nitrite in the presence of an inert solvent. The reaction is suitably employed for the production of higher nitroalkanes and results in the production of a single nitroalkane.

DETAILED DESCRIPTION In carrying out the process of the present invention,

nited States Patent "ice the alkyl nitrate and alkali metal nitrite are reacted under reaction conditions in the presence of an inert solvent.

The process is conducted at a temperature suflicient to obtain the nitroalkane but insufiicient to cause substantial ,decomposition of the nitroalkane. Temperatures below about 30 C. are generally not practical due to the slowrate of reaction, while temperatures above C. tend to cause substantial decomposition of the nitroalkane. A temperature in the range of from about 45 to about 70 C. is generally preferred.

The molar ratio of alkali metal nitrite to alkyl nitrate may be varied over a wide range, with a ratio of alkali metal nitrite to alkyl nitrate in the range of from about 2.0:1.0 to about 1.0:l.0 being typically employed. A molar ratio of alkali metal nitrite to alkyl nitrate of ap proximately 1521.0 to about 1.1:1.0 is preferred.

The process of the present invention is conducted in the presence of an inert solvent for the alkali metal nitrite and the alkyl nitrate. The amount of solvent employed should, of course, be sufiicient to dissolve both the alkali metalnitrite and the alkyl nitrate. Any suitable solvent which is inert to the reactants and the reaction products may be employed. Examples of suitable solvents include hexamethylphosphoramide (HMPA), dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), monomethyl formamide, and the like. Because of ready availability and the excellent results obtained therewith, DMSO and I-IMPA are preferred.

As previously indicated, the alkyl nitrate should be a primary or secondary alkyl nitrate, with primary alkyl nitrates being preferred. Alkyl nitrates containing from 1 up to about 20 carbon atoms are typically employed. Examples of such alkyl nitrates include butyl nitrate, propyl nitrate, octyl nitrate, ethylene glycol mononitrate, 2-octyl nitrate, decyl nitrate, Z-heptyl nitrate, 1,5-pentamethylene glycol dinitrate, phenylethyl nitrate, dodecyl nitrate, isopropyl nitrate, pentadecyl nitrate, 2-chloroethyl nitrate and the like.

Any suitable alkali metal nitrite may be employed in the process of the present invention. Examples of such suitable nitrites include sodium nitrite, potassium nitrite, and lithium nitrite. Because of its ready availability and the excellent results obtained therewith, sodium nitrite is preferred.

In order to prevent unwanted destruction of the nitroalkane by nitrite esters which are also formed during the reaction, it is preferred to employ a scavenger for these nitrite esters. The amount of nitrite ester scavenger used in the process will vary and will depend principally on the particular alkali metal nitrite, the particular alkyl nitrate, the solvent and the temperature employed. A molar ratio of nitrite ester scavenger to alkali metal nitrite in the range of from about 2.0: 1.0 to about 0.1 1.0 is typically employed with a molar ratio of from about 1.0:1.0 to about 0.5 :1.() being preferred. Any suitable nitrite scavenger may be employed. Examples of such suitable scavengers include the malonate esters such as ethyl malonate, phloroglucinol, catechol, resorcinol, and the like, with ethyl malonate being preferred. These scavengers are converted to their nitroso derivatives by reaction with the nitrite esters. The nitroso derivatives do not destroy the nitroalkanes.

The nitroalkanes prepared in accordance with the present invention may be recovered by any suitable procedure. For example, the recovery may be accomplished by distillation or by extraction with a suitable solvent, such as ethyl ether or petroleum ether followed by drying or distillation.

The invention will be understood more fully by reference to the following specific examples. It is understood that the examples are presented for the purpose of illus- 3 tration only and are not intended as a limitation of the invention.

Example 1 To a three neck reaction vessel equipped with thermometer, stirrer, condenser and heating mantle were charged 60 ml. of DMSO. To the DMSO were added 5.26 grams (0.05 mole) of propyl nitrate, 5.52 grams (0.08 mole) of sodium nitrite and 6.41 grams (0.04 mole) of ethyl malonate with stirring to form a solution. The resulting solution was then stirred for a period of two hours during which period the temperature of the solution was maintained at approximately 65 C. Upon completion of the reaction period, the resulting reaction mixture containing l-nitropropane was poured into a vessel containing water and then extracted with ethyl ether. The resulting mixture comprised an upper layer of ethyl ether and a lower layer of water. The layers were separated and the aqueous layer was twice extracted with ethyl ether. The ethereal layer and the ethereal extracts were combined, dried over anhydrous magnesium sulfate and distilled. l-nitropropane was obtained in a conversion of 40% based on the alkyl nitrate.

Examples 29 Additional examples of the preparation of nitro- We claim:

1. A process for the production of nitroalkanes which comprises reacting a primary or secondary alkyl nitrate with an alkali metal nitrite in the presence of an inert solvent at a temperature sulficient to obtain the said nitroalkane but insuflicient to cause substantial decomposition of the nitroalkane.

2. The process of claim 1 wherein the reaction is carried out in the presence of a nitrite ester scavenger.

3. The process of claim 1 wherein the temperature is in the range of from about to about 120 C.

4. The process of claim 3 wherein the temperature is in the range of from about to about 70 C.

5. The process of claim 2 wherein the nitrite ester scavenger is ethyl malonate.

6. The process of claim 1 wherein the molar ratio of alkali metal nitrite to alkyl nitrate is in the range of 2.0:1 to about 1.0:1.

7. The process of claim 2 wherein the molar ratio of scavenger to alkali metal nitrite is in the range of about 2.0:1.0 to about 0.1:1.0.

8. The process of claim 7 wherein the molar ratio of scavenger to alkali metal nitrite is in the range of about 1.0:l.0 to about 0.5:l.0.

9. The process of claim 1 wherein the solvent is hexamethylphosphoramide.

TABLE 1 Percent; conversion based Example Alkali metal on alkyl number Product; Alkyl nitrate nitrite Nitrate scavenger Solvent nitrate 2 l-nitrooetane Octyl nitrate Sodium nitrite Ethyl malonate DMSO 41 3 l-nitropropane Propyl nitrate do. Phl0rog1uc1nol DMSO 33 4 do d0 Lithium mtnte .do DMSO 37 6 do do Sodium nitrite..... Ethyl malonate. DMF 23 6. 2nitrooctane 2-oety1 nitrate... d do DMSO 11 7. 1-nitropropane Propyl nitrate None DMSO 16 8... z-ehloro-l-nitroetha 2-ohloroethylnitrate Ethyl ma1onate- DMSO 5 1,5-dinitropentane 16 and 1,5-pentamethy1ene glycol dimtrate d0 ..d0 DMSO 9(b) 5-nitro-l-pentane-ol 44 Example 10 Essentially the same procedure used in Example 1 is employed except that dodecyl nitrate is substituted for propyl nitrate to make l-nitrododecane.

Example 11 10. The process of claim 1 wherein the solvent is dimethyl sulfoxide.

References Cited UNITED STATES PATENTS 9/1965 Stengel et al 260-644 OTHER REFERENCES Astle, Industrial Organic Nitrogen Compounds, Reinhold Pub. Corp., New York, 1961, pp. 346, 347 and 375.

LELAND A. SEBASTIAN, Primary Examiner US. Cl. X.R. 

